Bioactive Hydrogels with Enhanced Initial and Sustained Cell Interactions

Abstract

The highly tunable properties of poly(ethylene glycol) (PEG)-based hydrogel systems permit their use in a wide array of regenerative medicine and drug delivery applications. One of the most valuable properties of PEG hydrogels is their intrinsic resistance to protein adsorption and cell adhesion, as it allows for a controlled introduction of desired bioactive factors including proteins, peptides, and drugs. Acrylate-PEG-N-hydroxysuccinimide (Acr-PEG-NHS) is widely utilized as a PEG linker to functionalize bioactive factors with photocrosslinkable groups. This enables their facile incorporation into PEG hydrogel networks or the use of PEGylation strategies for drug delivery. However, PEG linkers can sterically block integrin binding sites on functionalized proteins and reduce cell-material interactions. In this study we demonstrate that reducing the density of PEG linkers on protein backbones during functionalization results in significantly improved cell adhesion and spreading to bioactive hydrogels. However, this reduction in functionalization density also increases protein loss from the matrix over time due to ester hydrolysis of the Acr-PEG-NHS linkers. To address this, a novel PEG linker, acrylamide-PEG-isocyanate (Aam-PEG-I), with enhanced hydrolytic stability was synthesized. It was found that decreasing functionalization density with Aam-PEG-I resulted in comparable increases in cell adhesion and spreading to Acr-PEG-NHS systems while maintaining protein and bioactivity levels within the hydrogel network over a significantly longer time frame. Thus, Aam-PEG-I provides a new option for protein functionalization for use in a wide range of applications that improves initial and sustained cell-material interactions to enhance control of bioactivity.

Drying and storage effects on poly(ethylene glycol) hydrogel mechanical properties and bioactivity

“…Additionally, PEGDAA hydrogels containing acrylate-PEG-functionalized collagen or Scl2 (1X) were incubated at 37°C in PBS for 6 weeks with no differences in bioactivity compared to 1 day swelling. 59 These results indicate that the proteins are not denaturing in the timeframe of this study and that losses in bioactivity can solely be attributed to hydrolytic degradation of the protein linker.…”

“…Therefore, the reduction in bioactivity was attributed to degradation of the protein linker. In a related study, a significant reduction in protein retention was found on 0.5X Acr-PEG-functionalized collagen and Scl2 PEGDAA hydrogels after 6 weeks of swelling in PBS 59 . The reduction in protein retention led to corollary decreases in spreading for collagen and reduced adhesion and spreading for Scl2-2.…”

Bacterial collagen-like proteins that form triple-helical structures

“…However, for any ‘off the shelf’ product, sterilization and storage conditions are important. Recent studies have shown that dry storage of these modified materials is better than wet storage (Luong et al 2013), as under wet conditions, ester hydrolysis of the protein linker has been attributed to the slow loss of the bioactive collagen component (Luong et al 2013, Browning et al 2013). However, this problem can be potentially resolved through use of an alternative modification reagent, acrylamide-PEG-isosyanate (Browning et al 2013).…”

Myocardial matrix–polyethylene glycol hybrid hydrogels for tissue engineering

“…For example, the properties of collagen hydrogels were altered by cross-linking the protein-based hydrogel with multi-armed poly(ethylene glycol) (PEG) stars containing activated esters on the termini that reacted with amine residues on the protein [23]. PEG is an ideal candidate to add to protein hydrogels because it is biocompatible and inert [2, 33], and therefore the biochemical cues in the hydrogel remain the same. Herein, we demonstrate a new approach to tissue specific ECM-based hydrogels for tissue engineering by synthesizing myocardial matrix-PEG hybrid hydrogels by two different methods.…”